The AC adaptor may be incorrectly plugged into an outlet or the keyboard. Make sure that the AC adaptor is plugged in completely to the back of the keyboard's DC 9.5 V terminal that is labeled "DC 9.5V", and located between the "PHONES/OUTPUT" and "MIC IN/SAMPLING" ports. Additionally, make sure to fully plug the AC adaptor into a wall outlet. Try plugging the adaptor into another outlet if the first one does not work.

Check if there is any damage to the power cord such as visible wires or frayed plastic from winding or bending the cord. If the cord is plugged in completely to the DC 9.5 V terminal and has no visible damage, it may have internal damage or be faulty, thus needing to be replaced. New power supplies can be found at your nearest music store or online.

Ensure that there is nothing plugged into the black circular PHONES/OUTPUT (or headphone) terminal which is located on the back of the keyboard next to the "DC 9.5V" terminal. If not, then you may need to adjust the volume setting using the black volume slider located next to power button. If the sound still does not work, try turning the power off then back on again.

USB cable may not be completely plugged into each device. Try plugging the cable into another USB port on the computer, or try replugging the USB cable back into the black square USB port located on the back of the keyboard next to the "SUSTAIN" terminal.

Try turning off the keyboard and exiting the music software by pressing the "X" button to close the software. Turn the keyboard back on and restart the music software by double clicking on the software's icon.

Check if anything is stuck between the long white keys or the smaller black keys that would block them from being pushed down. If there is an object lodged between the keys, try to use your fingers to dislodge it. If nothing can be seen, it may be an internal issue, and the keys that are jammed must be replaced by following this repair guide.